U.S. patent number 5,433,206 [Application Number 08/267,247] was granted by the patent office on 1995-07-18 for system and a method for simultaneous, real time ultrasound imaging of biological tissue and measuring of blood flow velocity.
This patent grant is currently assigned to Elscint, Ltd.. Invention is credited to Arie Amara, Benjamin Sabbah.
United States Patent |
5,433,206 |
Sabbah , et al. |
July 18, 1995 |
System and a method for simultaneous, real time ultrasound imaging
of biological tissue and measuring of blood flow velocity
Abstract
A system for simultaneous, real time imaging of biological
tissue and measuring of blood flow velocities using the Doppler
principle resulting in an improvement in Doppler power spectrum of
the blood flow velocity measurements.
Inventors: |
Sabbah; Benjamin (Haifa,
IL), Amara; Arie (Mitzpe Gillon, IL) |
Assignee: |
Elscint, Ltd. (Haifa,
IL)
|
Family
ID: |
23017953 |
Appl.
No.: |
08/267,247 |
Filed: |
June 29, 1994 |
Current U.S.
Class: |
600/455 |
Current CPC
Class: |
G01S
15/8979 (20130101) |
Current International
Class: |
G01S
15/89 (20060101); G01S 15/00 (20060101); A61B
008/00 () |
Field of
Search: |
;128/660.01,660.05,661.08,661.09,661.10 ;73/861.25 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Manuel; George
Attorney, Agent or Firm: Sandler, Greeblum &
Bernstein
Claims
What is claimed is:
1. A system for simultaneous real time imaging of biological tissue
and measuring blood flow velocity, comprising:
a) an ultrasound transducer;
b) a signal generator for driving said ultrasound transducer
in:
(i) a scan mode of operation for imaging biological tissue and
(ii) a Doppler mode of operation for measuring blood flow velocity
where Doppler signals are missing when said ultrasound transducer
is driven in said scan mode of operation;
c) said signal generator including a randomizer for randomizing the
activation of said signal generator to operate either in the scan
mode or in the Doppler mode over random time periods;
d) a signal processor for receiving echo signals from said
biological tissue and from flowing blood; said signal processor
further processing said received echo signals to provide image
data;
e) a first display for displaying an image of biological tissue
based on said image data obtained from processing said echo signals
received from said biological tissue; and
f) a second display for displaying a Doppler power spectrum
representative of the blood flow velocity measurement based on said
echo signals received from said flowing blood and estimates of the
missing Doppler signals.
2. The system as in claim 1, wherein said randomizer randomizes the
activation of said signal generator between said scan and Doppler
modes of operation at a ratio of from about 1:2 to about 1:8.
3. The system as in claim 1, wherein said randomizer randomizes the
activation of said signal generator according to an equal
distribution function.
4. The system as in claim 3, wherein said equal distribution
function has a mean value of 4.
5. The system as in claim 5, wherein said equal distribution
function has a standard deviation from about 1 to about 3.
6. The system as in claim 1, wherein said randomizer randomizes the
activation of said signal generator according to a Gaussian
function.
7. The system as in claim 6, wherein said Gaussian function has a
mean value of 4.
8. The system as in claim 7, wherein said Gaussian function has a
standard deviation from about 1 to about 3.
9. The system of claim 1 further comprising:
a signal processor including a missing signal estimator for
estimating said missing Doppler signals.
10. The system as in claim 9, wherein said signal processor
estimates said missing Doppler signals using at least first order
interpolation.
11. A method for simultaneous, real time ultrasound imaging of
biological tissue and measuring of blood flow velocity comprising
the steps of:
examining a patient using an ultrasound transducer;
transmitting ultrasound signals from said ultrasound transducer in
a Doppler mode of operation for measuring blood flow velocity
during first time periods,
interrupting the Doppler mode of operation to use the ultrasound
transducer to perform a scan mode for imaging biological tissue
during second time periods, said Doppler signals being missing when
the ultrasound transducer operates in the scan mode of
operation
randomizing the length of the time periods during which the
ultrasound transducer is operated in the first and second time
periods;
receiving signals from said ultrasound transducer during both the
scan mode of operation and the Doppler mode of operation;
estimating the missing Doppler signals to provide estimated missing
Doppler signals;
processing said received signals to provide and refresh images of
biological tissue when said transducer is operating in the scan
mode;
processing said received signals to provide a Doppler power
spectrum representative of a blood flow velocity measurement when
the ultrasound transducer is operating in the Doppler mode; and
displaying images of the biological tissue based on the signals
received during the scan mode and displaying a Doppler power
spectrum based on the signals received and estimated when the
transducer is operating in a Doppler mode.
12. The method as in claim 11, wherein said step of randomizing
randomizes the driving of the transducer between the scan and
Doppler modes of operation at a ratio of from about 1:1 to about
1:8.
13. The method as in claim 12, wherein said step of randomizing
randomizes the driving of the transducer according to an equal
distribution function.
14. The method as in claim 13, wherein the equal distribution
function has a mean value of 4.
15. The method as in claim 14, wherein said equal distribution
function has a standard deviation from about 1 to about 3.
16. The method as in claim 11, wherein said step of randomizing
randomizes the driving of the transducer according to a Gaussian
function.
17. The method as in claim 16, wherein the Gaussian function has a
mean value of 4.
18. The method as in claim 17, wherein said Gaussian function has a
standard deviation from about 1 to about 3.
19. The method of claim 11, further comprising the step of
estimating the missing Doppler signals.
20. The method as in claim 19, wherein said step of estimating the
missing Doppler signals uses at least first order interpolation.
Description
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a system and a method for
simultaneous, real time ultrasound imaging of biological tissue and
measuring of blood flow velocity using the Doppler principle.
There exist in the marketplace devices for simultaneous ultrasound
imaging of biological tissue and measuring of blood flow velocities
based on the Doppler principle. The devices operate by time-sharing
an ultrasound transducer between scan and Doppler modes of
operation at a 1:1 ratio, that is, the ultrasound transducer is
driven in each mode alternately. Operating the device at a 1:1
ratio enables a real time image of the biological tissue to be
displayed, however, it restricts the upper velocity of blood flows
that can be measured to relatively low values. Attempts to measure
velocities greater than the upper limit produces the effect known
as aliasing.
Operating the devices at a 1:N ratio where N>1 enables the
velocities of fast flowing blood flows to be measured but entails
two disadvantages. First, the image of biological tissue is
refreshed at too slow a rate for real time imaging. Second, the
integrity of the Doppler power spectrum representative of the blood
flow velocity is impaired. This impairment is due to the estimation
of the Doppler signals which are missing when the device is
operating in scan mode as now described with reference to the
Doppler power spectrums shown in FIGS. 1a-1c.
The Doppler power spectrum shown in FIG. 1a displays a single
harmonic at approximately 1 kHz as rendered by driving the
ultrasound transducer at 8 kHz in the Doppler mode of operation
only. In comparison, the Doppler power spectrum shown in FIG. 1b
displays spurious harmonics at approximately -3 kHz, -1 kHz and 3
kHz in addition to the predominant 1 kHz harmonic as rendered by
driving the ultrasound transducer at 8 kHz at a 1:4 ratio between
the scan and Doppler modes of operation. The spurious harmonics can
be quantified as contributing to a missing signal estimator (MSE)
value of 4089.
To partly remedy this deterioration, the missing Doppler signals
are typically estimated as a function of measured Doppler signals.
Typical estimation techniques range from a simple linear
interpolation between two immediately adjacent measured signals to
more sophisticated estimation techniques as known in the art. As
evidenced by the Doppler power spectrum of FIG. 1c, even a linear
interpolation of missing Doppler signal manages to considerably
lower the MSE value from 4098 to 318.3. However, it will be noted
that the spurious harmonics in the Doppler power spectrum still
remain albeit at a reduced energy.
Therefore, it would be highly desirable to have a system and a
method for simultaneous, real time ultrasound imaging of biological
tissue and measuring of blood flow velocities using the Doppler
principle which improves the integrity of the Doppler power
spectrums of the blood flow velocity measurements.
It would also be highly desirable that the system and the method be
highly robust so as to be both equally applicable over a wide range
of pulse repetition frequencies and computationally simple.
SUMMARY OF THE INVENTION
The main object of the present invention is for a system and a
method for simultaneous, real time ultrasound imaging of biological
tissue and measuring of blood flow velocities using the Doppler
principle which improves the integrity of the Doppler power
spectrums of the blood flow velocity measurements.
Hence, according to one aspect of the present invention, there is
provided a system for simultaneous, real time ultrasound imaging of
biological tissue and measuring of blood flow velocity, comprising:
(a) an ultrasound transducer; (b) a signal generator for driving
the ultrasound transducer in i) a scan mode of operation for
imaging biological tissue, and ii) a Doppler mode of operation for
measuring blood flow velocity, in which Doppler signals are missing
when the ultrasound transducer operates in the scan mode of
operation; (c) a randomizer for randomizing the activation of the
signal generator; (d) a display for displaying an image of
biological tissue; and (e) a display for displaying a Doppler power
spectrum of a blood flow velocity measurement.
The randomizer randomizes the activation of the signal generator
between the scan and Doppler modes of operation at a ratio from
about 1:2 to about 1:8 according to an equal distribution function
or Gaussian function. The functions preferably have a mean value of
4 and a standard deviation from about 1 to about 3. The system also
preferably includes a signal processor for estimating the missing
Doppler signals using at least first order interpolation.
According to another aspect of the present invention, there is also
provided a method for simultaneous, real time ultrasound imaging of
biological tissue and measuring of blood flow velocity, comprising
the steps of: (a) providing an ultrasound transducer; (b) driving
the ultrasound transducer in: i) a scan mode of operation for
imaging biological tissue, and ii) a Doppler mode of operation for
measuring blood flow velocity, where Doppler signals are missing
when the ultrasound transducer operates in the scan mode of
operation; (c) randomizing the step of driving; (d) displaying an
image of biological tissue; and (e) displaying a Doppler power
spectrum representative of a blood flow velocity measurement.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is herein described, by way of example only, with
reference to the accompanying drawings, wherein:
FIG. 1a shows the Doppler power spectrum of a blood flow velocity
measurement as rendered by a transducer driven at 8 kHz in the
Doppler mode of operation only;
FIG. 1b shows the Doppler power spectrum of a blood flow velocity
measurement as rendered by a transducer driven at 8 kHz in a
conventional 1:4 time-shared fashion between the scan and Doppler
modes of operation;
FIG. 1c shows the Doppler power spectrum of FIG. 1b improved by
using linear estimation for estimating missing Doppler signals;
FIG. 2 shows a system for simultaneous, real time ultrasound
imaging of biological tissue and measuring of blood flow velocity
using the Doppler principle according to the teachings of the
present invention; and
FIG. 3 shows the Doppler power spectrum of FIG. 1c improved by the
use of system of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is of a system and a method for simultaneous,
real time ultrasound imaging of biological tissue and measuring
blood flow velocity using the Doppler principle.
The system and the method are particularly designed to remove the
spurious harmonics from the Doppler power spectrum rendered when an
ultrasound transducer is driven in a conventional time-shared
fashion between scan and Doppler modes of operation.
The principles and operation of the system and the method according
to the present invention may be better understood with reference to
the drawings, which are illustrative only, and which demonstrate
examples of various aspects of the system and the method according
to the present invention.
Referring now to the drawings, FIG. 2 illustrates a system,
generally designated 10, constructed and operative according to the
teachings of the present invention, for simultaneous, real time
ultrasound imaging of biological tissue and measuring of blood flow
velocity using the Doppler principle.
System 10 includes a signal generator 12 for driving an ultrasound
transducer 14 for transmitting and receiving ultrasonic energy in a
time-shared fashion between a scan mode of operation for imaging
biological tissue and a Doppler mode of operation for measuring
blood flow velocity.
In sharp contrast to conventional systems described in the
Background of the Invention in which ultrasound transducer 14 is
activated at a fixed ratio between the scan and Doppler modes of
operation, it is a particular feature of the present invention that
system 10 also includes a randomizer 16 for randomizing the
activation of signal generator 12. The benefit of randomizing the
time sharing of transducer 14, thereby establishing temporally
randomized missing Doppler signals when transducer 14 is driven in
the scan mode of operation, is explained below with reference to
FIG. 3.
A wide range of discrete functions can be implemented by randomizer
16 including, but not limited to, an equal distribution function, a
Gaussian function, etc. Preferably, discrete functions having mean
values of 4 and a standard deviation of 1, 2 or 3 are implemented
although means values from about 2 to about 8 can also be used. It
can be readily appreciated that randomizer 16 is equally operable
over a wide range of pulse repetition frequencies.
A signal processor 18 processes the signals received by transducer
14 to produce an image 20 of scanned biological tissue typically
shown on a 512.times.512 display 22 and a Doppler power spectrum 24
of blood flow velocities displayed on a display 26. The excursion
of points 28 from the x axis of Doppler power spectrum 24 is
representative of its frequencies.
As described in the Background of the Invention, signal processor
18 preferably estimates the missing Doppler signals as a function
of measured Doppler signals proximate to the missing Doppler
signals by any one of a wide range of estimation techniques. Such
techniques range from simple linear interpolation between two
immediately adjacent measured Doppler signals to more sophisticated
estimation techniques, for example, as performed by the Missing
Signal Estimator described in accordance U.S. Pat. No. 4,934,373
entitled "Method and Apparatus for Synthesizing a Continuous
Estimate Signal from Segments of a Gaussian Signal Provided by
Ultrasonic Doppler Measurement on a Fluid Flow" which issued on 19
Jun. 1990.
The improved integrity of the Doppler power spectrum as rendered by
randomizing the activation of signal generator 12 can be clearly
seen on comparing Doppler power spectrum 24 to the Doppler power
spectrums shown in FIGS. 1a and 1c. The comparison reveals that
Doppler power spectrum 24 has a contour closer to that of FIG. 1a
than FIG. 1c as evidenced by it having only one harmonic frequency.
In particular, using the same 8 kHz Doppler frequency as described
above, system 10 renders Doppler power spectrum 24 having a
harmonic frequency at approximately 1 kHz and a greatly reduced MSE
value of 92.78.
While the invention has been described with respect to a limited
number of embodiments, it will be appreciated that many variations,
modifications and other applications of the invention may be
made.
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